This invention relates to transmission controls and, more particularly, to electro-hydraulic controls for controlling both a torque converter clutch and shifting clutches in a transmission.
Many of the vehicles produced today employ either a multi-ratio or continuously-variable ratio transmission that includes both a torque converter clutch and at least one shifting torque transmitting mechanism such as a friction clutch or friction brake. The torque converter clutch is engaged to directly connect the torque converter input member (impeller) with the torque converter output member (turbine). This is undertaken to improve the efficiency of the powertrain and therefore improve the fuel economy by reducing the slip loss within the torque converter.
The shifting torque transmitting mechanisms are fluid-operated devices generally of the friction plate type. The engineering community has termed these devices as xe2x80x9cclutchesxe2x80x9d whether they are rotating torque transmitting mechanisms or stationary torque transmitting mechanisms. These devices are engaged in a controlled fashion to enable smooth vehicle launch or to minimize torque disturbances in the driveline during ratio interchanges.
In conventional electro-hydraulic controls, the torque converter clutch and the shifting torque transmitting mechanisms have separate control circuits. The torque converter clutch control generally includes a pulse width modulated (PWM) solenoid and a regulator valve. The torque transmitting mechanism control generally incorporates a variable bleed solenoid (VBS) and a regulator. Both of these types of control mechanisms require space within the transmission control and add weight to the vehicle. The torque converter clutch control also includes a valve mechanism for reversing the flow of hydraulic fluid through the torque converter during torque converter clutch engagement.
It is an object of this invention to provide an improved hydraulic control system for a power transmission.
In one aspect of the present invention, the power transmission includes both a torque converter clutch and at least one shifting torque transmitting mechanism that are controlled during engagement. In another aspect of the present invention, a single variable pressure control solenoid valve is provided to control the rate of pressure change in both the torque converter clutch and the torque transmitting mechanism during engagement. In yet another aspect of the present invention, an engagement control valve is moveable to a pressure set position to selectively direct a controlled apply pressure to the torque converter clutch and to a spring set position to control the torque transmitting mechanism individually and independently.
In still anther aspect of the present invention, the engagement control valve is operable to direct a maintenance pressure to the torque transmitting mechanism while engaging the torque converter clutch. In yet still another aspect of the present invention, a torque converter clutch regulator valve is controlled by the variable pressure solenoid valve to establish the engagement pressure for the torque converter clutch and a torque transmitting mechanism regulator valve is controlled by the variable pressure control solenoid valve to establish the engagement pressure for the torque transmitting mechanism.
In a further aspect of the present invention, a flow direction valve is positionable to supply the torque transmitting mechanism engagement pressure to either a forward torque transmitting mechanism or a reverse torque transmitting mechanism. In yet a further aspect of the present invention, both the variable pressure control solenoid valve and the engagement control valve pressure set position are controlled by electrical signals. In a still further aspect of the present invention, engagement pressure is supplied selectively to the torque transmitting mechanisms when a discontinuance of the electrical signals occurs.